Process for making ceramic compositions



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Patented Dec. 1, 1931 UNITED STATES.

PATENT OFFICE @RPOBATION', OF- HUNTINGTON PARK, CALIFORNIA P1 106138 FORMAKING- COMPOSITIONS No Drawing. Original application filed June 22,1926, Serial No. 117,869. Divided and this application filed February18, 1929. Serial No. 341,039.

This invention relates to improvements in the art of ceramics, and moreparticularly, to the preparation of cermic substances for improving thecharacter and quality of thefinished ceramic bodies.

The primary object is the production of a ceramic material which may bereadily combined with other ceramic" materials, such as fired clay in aplastic state, which after proper preparation and firing, will result ina product of superior capacity and stability.

A more detailed 'object is the production of such a modified compositionfor ceramic bodies having the further distinctive peculiarity oftremendously increasing the breaking point strength of the finalproduct, and correspondingly increasing tensile and compression strengththereof.

More in detail, the invention contemplates the release of aluminumsilicate crystals from I appropriate sources such as cyanite' andconditioning the same for specific growth in the direction of theirlongitudinal axis when fired after mixing with other ceramic materials.

The invention further comprises special novel treatment or treatments ofthe mineral substances employed for my purposes of clay strengthening;the utilization of an aluminum silicate the fibrous structure ofvwhichis derived mainly from cyanite crystals which possess theuniquecharacteristic of rowingin length, whilst not materially c angingin thickness under the action of predetermined heat control; and'thehandling of the said cyanite crystals according to special processes andcontrolled conditions to obtain the composition therefrom useful for thepurposes of the invention as outlined herein.

In order to develop clearly the utility of my invention in theindustrial arts, I first note that it is exceedingly important in theproduction of various clay products to increase the impact strength, orresistance to blows and the tensile and compressive.

strengths of such products. It is also highly important in such productsfor many purposes to render the products stable at high temperature asby decreasing as much as possible the shrinkage action of the bond claywithout decreasing its strength. By reducing such shrinkage, thecracking and warpage of the articles produced in the process of'manufacture, may be so greatly decreased as to do away withmanufacturing losses resulting from defective final products.

Without referring, to the more complex porcelains and vitreous bodies,it is desirable to explain at this time just how the elements of anordinary clay product structure are tensile, cross-breaking orcompressive loads depends entirely. upon the strength and thebrittleness of the glassy cement which holds the particles of theproduct together. Moreover, this cementing glass varies widely in itscharacteristics according to its composition,

extent of annealing when the ware is cooling in the kiln, and otherthings that need not be particularly mentioned.

In practical experience therefore, we come upon two pieces of burnt clayware substantially identical in appearance but which may have widelydifferent strengths. I have found for instance that terra cotta productsseparately manufactured in the sariie clay district may in one instancehave a difi'erence in break factor "of as much as 980 to 186.

The manufacturers, moreover, may be competingin the same market. Thedifierence in the break factor is due to the fact that the .glass of oneclay product has a much greater ing or strengthening clay productsconsists of cyanite, a mineral of the sillimanite group a of aluminumsilicates.

Cyanite possesses a fibrous structure as it occurs in nature. By heatingthe cyanite to a temperature and fora suflicient length of time to causeceramic cone 4 to be brought down, the typical cyanite crystals under 0a change which is unique in the minerals c ass. In other words, thefibres grow considerably in length but they do not change materially intheir thickness. The same phenomenon as to growth of the fibres appearsat temperatures above cone 4 with increasing eifects and usuallycomplete stability is reached at about cone 18 at which temperature thelengths of the fibres stop growing, and between this temperature andcone 36, no appreciable change in length takes place.

Above cone 36, melting ensues at which time the fibres will lose theiridentity.

The characteristic elongating growth of fibres of cyanite is availed ofby my invention, and as cyanite is a mineral obtainable in largequantities, it is highly desirable to utilize the same for the purposeof strengthening clay products and otherwise predetermining theproduction of such products in a manner to do away with wastage andlosses incident to defective manufacture.

Cyanite ore, if reduced to a powder, will be broken into angular fabricsrather than fibres, so pulverization is therefore not resorted to.According to my invention, I heat the cyanite ore to a temperatureapproximating between 1700 degrees F. to 1800 degrees F., largelydependent upon the character of the ore as mined. This temperatureshould be suflicient to drive 011: the usual small traces of crystallinewater, and to-only start the elongation phenomenon previously referredto as-creating the fibrous growth of which I desire to avail.Additionally, this temperature will change the structure of the quartzgangue associated with the cyanite ore to fracture the quartz away fromthe cyanite readily. In this way, I break down the cyanite fibres intoindividual slender shafts. Then by table concentration with water, the

fibres "may be brought topractically any desired composition or ratio ofquartz and other ingredients such as pyrophyllite and possibly otherminerals included with the said cyanite. By additional milling of thecyanite fibres, they will be merely broken apart, but their structurewill be unchanged materially. By the above steps of my process of makingmy composition, the production of rounded pieces or particles of cyaniteis absolutely minimized.

In carrying forward my process, I maintairi a reducing temperatureduring the roasting operation above referred to, and in this Way, I amenabled not only to accelerate the change in structure to produce thefibres, but I obtain an additional result, i. e., render the iron oxidebearin components of the ore magnetic so that t ey may be readilyseparated from the rest of the produce by employing standard typemagnetic concentrators. Y

The removal of the iron oxide bearing components of the ore to a greateror less extent controls its purity and color, and since these factorsare of importance to the ultimate clay product with which my compositionmay be combined, the said control is highly desirable from thestandpoint of practical manufacture.

In lieu of employing the table concentration method of controlling thedesired ultimate composition of 111 product as respects the ratio ofcyanite bres to quartz and other substances, I may use a totallydifi'erent method or process of separating the fibres minerals referredto. ess to which I now refer consists in subjecting the crude cyaniteore to a very sudden change in temperature by plunging the'red hotcharge of the same as it comes from the conveyer into cold Water. Inthis way, the cyanite crystals are not shattered by the quenching of therock, but the surrounding quartz gangue is converted into a soft granular material that renders the rock so friable that it may be brokenapart by pressure of the fingers. By this quenching process, the cyanitecrystals may be readily cleared of the attached particles of quartz,etc., in a very thorough and effective manner, and the subsequentconcentration of the material may be readily performed. After thequenching of the crude ore as described, it is only necessary to crushthe material as by the use of a swing hammer or any suitable impact typeof mill, and then by screening the crushed product as much of the gangueor quartz may beremoved as may be desired, by only the screeningoperation. The relatively pure cyanite fibres'will remain on the screenand thequartz or gangue will pass through as a sand, having somewhat thecharacteristics of granulated sugar; This method of separation of thecyanite fibres from the gangue .to a greater or less extent from theattached The alternative proc- .interweavingwithin the mass of or quartzor other associated unneeded minerals is to be preferred to that firstdescribed,

- as it reduces the cost of the processing operation, and avoids thenecessity of resorting to table concentration with water.

Having in view the desirability of increasing the strength of burnt clayproducts, by

glass cemented particles of the product, insoluble, inert and strongfibreswhich will reinforce the glassy cement, the action of mycomposition when added to the clay product will accomplish the objectabove outlined. The plastic mass of clay should have the strengtheningcomposition of this invention added in predetermined useful proportionswith respect to that of the mass. The clay mass includes particles ofrelatively pure clay substance of a colloidal nature including manyimpurities such as fine sand, mica, iron pyrites, rock of uncertaincomposition, clay which is relatively pure but often not sulficientlyfine to be plastic, and to this mass of clay my strengtheningcomposition will be added. The same composition is in the form, of apowder consistin of the slender fibrous crystals of cyanite p usassociated adulterants which will function in a'manner hereinafter to beset forth.

,;When my strengthening composition and the clay are moistened, puggedto proper con- 'sistency, molded, dried, and fired, peculiar changes inthe structure of the combined mass takes place. As the temperatureincreases in the firing, the free remaining water or moisture is ofcourse expelled. Later, the chemical or combined water passes off at"higher temperature. At this stage plasticity is destroyed and themixture is then no longer clay because its colloids have been changedwith the loss of its clay-like properties. Further increase oftemperature causes contained organic matter, such as decayed ve etationto oxidize and leave pore spaces. ecessarily, if something to counteractsuch change were notpresent, fire shrinkage would immediately ensue. Mystrengthening composition, it will be recalled, however, includes theslender shafts or fibres, and these start to grow in length as theoxidation of the organic substances carried by the clay takes place, andat the same time, the temperature increases so that the various admixedimpurities start to soften and form the various glass or cementingcompositions that have been previously referred to. v

By reason of the provision of the growing fibres of my strengtheningcomposition, the

fire shrinkage which would ordinarily ensue.

as thel cementing glames form and the clay particles being to coalesce,does not take place as would be the case where the fibres do notelongate as described. The elongation or growing holding apart the clayparticles but causingthe glass to surround the same and up over, that bysimply proper proportioning of my strengthening composition with themass of clay used, I am enabled to effect a complete equilibrium suchthat there is neither expansion, nor shrinkage caused in the firing ofthe product.

The final fired clay body, including my strengthening composition willthus comprise a massof clay particles interspersed with thestrengthening fibres or reinforcing slender shafts growing in the voidsleft by the exit of water and organic matter, the said fibres and theclay particles cemented together in the interstices with the glass thatordinarily forms the only bond between said particles.

With my invention in practice, the characteristic of brittleness from acorrectly proportio ed and fired clay product containing my I product, Iobtain a cement which is reinforced with a mass -of interwoven fibresand the physical structure of the usual or common burnt clay body iscompletely changed. 7

I have found that the extent to which my strengthening compositionshould be employed for best commercial results varies. for difierentkinds of clay products. It is usually necessary to determine by studythe facts of the strengthening composition with a par-. ticularcomposition of clay product body. Such clay products may roughlybe'classified as follows 1.- Products too low to bring. about thecharacteristic elongation of cyanite fibres in the maturingtemperatures, and therefore not advantaged by the use of my composition,

such as red brick, paving brick, flower pots,

etc.

2. Products maturing at temperatures from Gone 4 to Cone 12 andembracing all large tonnage types exclusive of the first mentionedabove.

3. Products maturing from temperatures from Gone 12 to Gone 18 in whichmay be included fine porcelains, heavy duty saggers, etc.

refractory wares,

My strengthening composition as com posed. i

and processed in the manner herein described is especially useful forproducts of the second class above referred to. The cyanite crystalsbear a definite relation to the other ingredients of the finishedproduct. The function of the adultering ingredients is to hold down therefractoriness of the product to an extent that the addition of mycomposition the standard bodies maturing at temperature minimums of Cone4 and maximums of Cone 12 will not be rendered so refractory that anactual loss of strength is caused instead of gained. I have found thatthe addition of pure cyanite powder to a terra cotta body maturing atCone 6 will reduce the strength to a marked degree, whereas the additionof 20% of my specially repared cyanite composition, even though it e ofinferior purity, strengthens certain terra cotta bodies as much as2200%.

My strengthening composition as prepared for the market may be of aformula according to the following notation, though I do not wish to belimited, of course, to the exact propositions specified, as they aremerely typical of the strengthening product that gives the greatestvalue as to strengthening effect, in typical terra cotta, stone ware,sagger, low-fire refractory ware, and similar bodies fired to Cone 4 onthe low side, and Gone 12 on the high side.

Per cent Crystals of pure cyanite 68 Crystals of turmaline 11 -Cyanitecrystals imbedded in quartz 7 Free quartz fra ents 4 Crystals ofpyrophyllite and associated impurities 10 This is a divisionalapplication of the parent application, Serial .No. 117,869, filed June22nd, 1926.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of'the United States is 2- 1. The process ofmaking a clay product strengthening ceramic composition, comprisingheating a crystalline mineral body of, cyanite to a temperaturesuflicient to change the structure of attached minerals to fracture theminerals readily away from the cyanite,

, ture of attached minerals to fracture the m llerals readily away fromthe crystalline body but not exceeding approximately 1800 F. to commenceelongation of its crystals and facilitate the separation of attachedminerals, and separating therefrom said attached minerals to such anextent as to control the relative proportions of the crystalline bodyand said minerals, whereby the adulterating infiuence of the attachedminerals ma be utilized to control the de cc of fire s rinkage of aproduct with w oh the composition may be fired. v

i 3. The process of making a clay product strengthening ceramiccomposition, comprising heating a crystalline mineral body to atemperature of from approximately 1700 to 1800 F. to commence elongationof its crystals and facilitate the separation of attached minerals, andseparating therefrom said attached minerals, and maintaining a'reducingatmosphere during the roasting operation, to

accelerate the crystal elongation action, and to render any ironoxide-bearing components of the ore magnetic, whereby magneticseparation may be employed to remove such components.

4. The process of makinga ceramic composition of the class described,comprising heating a body of ore of cyanite and attached minerals to atemperature of from approximately 1700 F. to approximately 1800 F. tostart the elongation of the fibrous crystals of cyanite, separating outthe attached minerals to an extent desired, and maintaining a reducingatmosphere during such heating to render iron oxide-bearing componentsof the body magnetic to facilitate magnetic separation thereof.

5. The process of making a ceramic composition of the class described,comprising heating a body of ore of cyanite and attached minerals to atemperature of from approximately 17 00 F. to approximately 1800 F. tostart the elongation of the fibrous crystals of cyanite, and plunging ahot charge of the ore into cold water to shatter the attached mineralsand facilitate separation thereof, and then screening the product toremove the attached minerals to any desired extent to proportion them ina certain relation to the cyanite.

6. The process of making a ceramic composition of the class described,comprismg heating a body of ore of cyanite and attached minerals to atemperature sufiiciently high to change the structure of the ore, butnot exceeding 1800 F. to start the elongation of the fibrous crystals ofcyanite and to render the attached minerals readily fracturable awayfrom the cyanite crystals, and plunging a hot charge of the ore intocold water to shatter the attached minerals and facilitate separationthereof, removing the attaching mlnerals to an extent desired,-thenmaintaining the ore in a reducing atmosphere to render iron oxidebearing components thereof magnetic.

7. The process of makin a ceramic composition of the class descrlbed,comprising heating a body of'oreof cyanite and attached minerals to atemperature offrom approximately 1700 to approximatel 1800 F. to startthe elongation of the fi rous crystals aesaa 1e of cyanite and to rendeithe attached min 7 anite, plunging a hot charge of the ore into; coldwater to shatter the attached minerals erals readily fracturable awayfrom the cy and facilitate separation thereof; and then screening theproduct to remove the attached minerals to any desired extentto'proportion them in a certain relation to the cyanite, and

then milling the composition'to reduce it to powder. Intestimony whereofI aifix my signature.

THOMAS S. CURTIS

